As the demand for an electronic devices, such as computers, cellular phones, PDA, etc is increasing recently, an importance of a printed circuit board (PCB) using a surface mount technology (SMT) is increasing.
An apparatus for measurement of a surface profile capturing a surface profile of the PCB is used as a test device among devices composing the SMT inline system. The apparatus for measurement of the surface profile is used for detecting errors, such as a component mounting error, a soldering default, a short circuit, etc. which are occurred while the PCB is manufactured.
The apparatus for measurement of the surface profile capturing a surface profile of the PCB, installed in the SMT inline system is divided into a type of using an area-scan camera and a type of using a line-scan camera. Generally, the type of using the area-scan camera is widely used.
Meanwhile, as shown in FIG. 1, Bayer filters are attached in each pixel of a color camera used for the apparatus for measurement of surface profile, and red filters, green filters or blue filters of the Bayer filters are not adjacent to each other in each pixel.
Herein, information of three colors (R, G, and B) of each pixel is needed for making a color image using the color camera. However, one pixel of the color camera has only R or G or B information in actuality. Therefore, as shown in FIG. 2, besides one color information obtained directly from the pixel, another two color information are obtained by interpolation of the color information of adjacent pixels. FIG. 2 illustrates an example of the interpolation. The color camera is applied to a moiré system which is an apparatus for measurement of the surface profile for capturing 3D image.
Generally, 3D measurement using a moiré pattern is achieved by obtaining images while moving a grating more than 3 times at a predetermined distance in the state that the light is illuminated to the object through the grating and by detecting changes in a brightness of a measuring point. Thus, one of the key points of 3D measurement using the moirépattern is how accurately the changes in the brightness of the measuring point or the pixel can be detected.
Generally, it is difficult to use a one-color light as a light source in 3D soldering test using the moiré pattern. For example, if a blue-color light as the light source is used for measuring red-colored surface of the PCB, the camera can't detect the light reflected from the surface of the PCB and the changes in the brightness, because a only red-color light can be reflected from surface of the PCB. Therefore, it is impossible to measure the red-colored surface of the PCB in 3D using the blue-color light as the light source.
Accordingly, a white light is used as the light source of the apparatus for measurement of the surface profile having the type of moiré 3D. However, only one of the red-color information, the green-color information and the blue-color information can be obtained from each pixel although the white light is used, the blue-color information or the green-color information is only obtained from the 66.66% pixels, with the consequence that the result of the 3D measurement cannot be relied on.
Meanwhile, the necessity of the color image is important in 2D measurement, similarly to 3D measurement as described above. Also, the color image is very important in the 2D measurement using a combined 2D and 3D measuring apparatus.
And, in case of an apparatus for the soldering test using the 2D measurement, the color image obtained by using a top lighting and a side lighting is very important for accurately discriminating the solder. However, the surface of the PCB is provided with various color. Furthermore various color contrasted with each other is painted on the surface of one PCB. Thus, the color image of which information are three times as large as that of the black-and-white image is available for discriminating the solder in 2D measurement.
Also, an inspector inspects the 2D image and the 3D image by his eyes generally and determines whether the PCB is NG or not. However, because a boundary between the solder and a pad is obscure in 2D black-and-white image, it is important that the inspector can be made to draw an accurate conclusion using 2D color image.
In spite of the importance of the color image in the apparatus for measurement of the surface profile as mentioned above, the color camera has defects, such as expensiveness and slow capture speed as compared with the black-and-white camera.
Thus, the black-and-white camera is actually and widely used in 2D or 3D apparatus for measurement of the surface profile. Also, the black-and-white camera is mainly used in the 3D measuring apparatus using the moirépattern, because a reliability of the 3D measuring result is low in spite of using the white light as described above.
However, the black-and-white camera is applied to the 3D measuring apparatus using the moiré pattern which has the type of the combined measuring apparatus available of 2D measurement with the view to the high effective value of the 3D measurement and the low cost. Accordingly, the effectiveness of the 2D measuring result is low because the boundary between the solder and the pad is obscure in the 2D black-and-white image in the 2D measurement, with the consequence that the effectiveness the 3D measuring apparatus using the moiré pattern as the 2D and 3D combined measuring apparatus is low.